Biology MICROBES AS BIO CONTROL AGENTS AND BIO FERTILISERS

### sedEY TOPICS

star Microbes as Biocontrol Agents
star Agents used for Biocontrol
star Microbes as Bioffertilisers

### MICROBES AS BIOCONTROL AGENTS

● color{Violet}"Biocontrol" refers to the use of color{Violet}"biological methods" for controlling plant diseases and pests.

● In color{Violet}"modern society", these problems have been color{Violet}"tackled increasingly" by the use of chemicals – by use of color{Violet}"insecticides and pesticides".

● These chemicals are color{Violet}"toxic" and color{Violet}"extremely harmful", to human beings and animals alike, and have been color{Violet}"polluting our environment" (soil, ground water), fruits, vegetables and crop plants.

● Our soil is also color{Violet}"polluted" through our use of color{Violet}"weedicides" to remove weeds.

● color{Violet}"Biological control" of pests and diseases: In color{Violet}"agriculture", there is a method of controlling pests that relies on color{Violet}"natural predation" rather than introduced chemicals.

● A color{Violet}"key belief" of the organic farmer is that color{Violet}"biodiversity furthers health".

● The more variety a color{Violet}"landscape" has, the more color{Violet}"sustainable" it is.

● The color{Violet}"organic farmer", therefore, works to create a system where the color{Violet}"insects" that are sometimes called color{Violet}"pests" are not eradicated, but instead are kept at color{Violet}"manageable levels" by a complex system of color{Violet}"checks and balances" within a living and vibrant ecosystem.

● Contrary to the color{Violet}"conventional farming practices" which often use chemical methods to kill both color{Violet}"useful and harmful life" forms indiscriminately, this is a color{Violet}"holistic approach" that seeks to develop an understanding of the color{Violet}"webs of interaction" between the myriad of organisms that constitute the field color{Violet}"fauna and flora".

● The color{Violet}"organic farmer" holds the view that the color{Violet}"eradication" of the creatures that are often described as color{Violet}"pests" is not only possible, but also color{Violet}"undesirable", for without them the color{Violet}"beneficial" predatory and parasitic insects which depend upon them as food or hosts would color{Violet}"not be able to survive".

● Thus, the use of color{Violet}"biocontrol measures" will greatly color{Violet}"reduce our dependence" on toxic chemicals and pesticides.

● An color{Violet}"important part" of the biological farming approach is to color{Violet}"become familiar" with the various life forms that inhabit the field, color{Violet}"predators as well as pests", and also their life cycles, patterns of feeding and the habitats that they prefer.

● This will help develop color{Violet}"appropriate means" of biocontrol.

### AGENTS USED FOR BIOCONTROL

● The very familiar beetle with red and black markings – the color{Violet}"Ladybird", and color{Violet}"Dragonflies" are useful to get rid of color{Violet}"aphids and mosquitoes", respectively.

● An example of microbial biocontrol agents that can be introduced in order to control color{Violet}"butterfly caterpillars" is the bacteria color{Violet}"𝘉𝘢𝘤𝘪𝘭𝘭𝘶𝘴 𝘵𝘩𝘶𝘳𝘪𝘯𝘨𝘪𝘦𝘯𝘴𝘪𝘴" (often written as color{Violet}"Bt" ).

● These are available in color{Violet}"sachets as dried spores" which are mixed with water and sprayed onto color{Violet}"vulnerable plants" such as brassicas and fruit trees, where these are eaten by the color{Violet}"insect larvae".

● In the gut of the larvae, the color{Violet}"toxin is released" and the color{Violet}"larvae get killed".

● The bacterial disease will color{Violet}"kill the caterpillars", but leave color{Violet}"other insects unharmed".

● Because of the development of color{Violet}"methods of genetic engineering" in the last decade or so, the scientists have introduced B. 𝘵𝘩𝘶𝘳𝘪𝘯𝘨𝘪𝘦𝘯𝘴𝘪𝘴 toxin color{Violet}"genes into plants".

● Such plants are color{Violet}"resistant to attack" by insect pests.

● color{Violet}"Bt-cotton" is one such example, which is being cultivated in color{Violet}"some states" of our country.

● A color{Violet}"biological control" being developed for use in the treatment of plant disease is the color{Violet}"fungus 𝘛𝘳𝘪𝘤𝘩𝘰𝘥𝘦𝘳𝘮𝘢".

● 𝘛𝘳𝘪𝘤𝘩𝘰𝘥𝘦𝘳𝘮𝘢 species are color{Violet}"free-living fungi" that are very common in the color{Violet}"root ecosystems".

● They are color{Violet}"effective biocontrol agents" of several plant pathogens.

● color{Violet}"Baculoviruses" are pathogens that color{Violet}"attack insects" and other arthropods.

● The majority of baculoviruses used as color{Violet}"biological control agents" are in the genus color{Violet}"Nucleopolyhedrovirus".

● These viruses are excellent candidates for color{Violet}"species-specific", color{Violet}"narrow spectrum" insecticidal applications.

● They have been shown to have color{Violet}"no negative impacts" on plants, mammals, birds, fish or even on non-target insects.

● This is especially desirable when color{Violet}"beneficial insects" are being color{Violet}"conserved'" to aid in an overall color{Violet}"integrated pest management (IPM) programme", or when an ecologically sensitive area is being treated.

### MICROBES AS BIOFERTILISERS

● With our present day life styles environmental color{Violet}"pollution" is a major color{Violet}"cause of concern".

● The use of the color{Violet}"chemical fertilisers" to meet the ever-increasing demand of color{Violet}"agricultural produce" has contributed significantly to this pollution.

● Of course, we have now realised that there are problems associated with the color{Violet}"overuse of chemical fertilisers" and there is a large pressure to switch to color{Violet}"organic farming" – to use of color{Violet}"biofertilisers".

● Biofertilisers are organisms that color{Violet}"enrich the nutrient quality" of the soil.

● The color{Violet}"main sources" of biofertilisers are color{Violet}"bacteria", color{Violet}"fungi" and color{Violet}"cyanobacteria".

● You have studied about the color{Violet}"nodules" on the roots of color{Violet}"leguminous plants" formed by the symbiotic association of color{Violet}"Rhizobium".

● These bacteria color{Violet}"fix atmospheric nitrogen" into organic forms, which is used by the plant as color{Violet}"nutrient".

● Other bacteria can color{Violet}"fix atmospheric nitrogen" while free-living in the soil (examples color{Violet}"𝘈𝘻𝘰𝘴𝘱𝘪𝘳𝘪𝘭𝘭𝘶𝘮" and color{Violet}"𝘈𝘻𝘰𝘵𝘰𝘣𝘢𝘤𝘵𝘦𝘳"), thus enriching the nitrogen content of the soil.

● Fungi are also known to form color{Violet}"symbiotic associations" with plants (color{Violet}"mycorrhiza").

● Many members of the genus color{Violet}"Glomus form mycorrhiza".

● The color{Violet}"fungal symbiont" in these associations color{Violet}"absorbs phosphorus" from soil and passes it to the plant.

● Plants having such color{Violet}"associations" show other benefits also, such as resistance to color{Violet}"root-borne pathogens", tolerance to color{Violet}"salinity and drought", and an overall increase in color{Violet}"plant growth and development".

● color{Violet}"Cyanobacteria" are autotrophic microbes widely distributed in aquatic and terrestrial environments many of which can fix atmospheric nitrogen, e.g. color{Violet}"𝘈𝘯𝘢𝘣𝘢𝘦𝘯𝘢, 𝘕𝘰𝘴𝘵𝘰𝘤", color{Violet}"𝘖𝘴𝘤𝘪𝘭𝘭𝘢𝘵𝘰𝘳𝘪𝘢," etc.

● In color{Violet}"paddy fields", cyanobacteria serve as an important color{Violet}"biofertiliser".

● color{Violet}"Blue green algae" also add organic matter to the soil and color{Violet}"increase its fertility".

● Currently, in our country, a number of color{Violet}"biofertilisers are available commercially" in the market and farmers use these regularly in their fields to color{Violet}"replenish soil nutrients" and to reduce dependence on color{Violet}"chemical fertilisers".